Characterization of tellurium nanorods synthesised by Halogeometricum borinquense E3 and evaluation of their antioxidant, antimicrobial and biocompatibile properties.

Extremely halophilic archaea are well adapted to salt-saturated environments. It was of interest to investigate their response to multiple stresses like chalcogen tolerance coupled to high salinity. In the present study, the haloarchaeon Halogeometricum borinquense E3 was evaluated for potassium tellurite tolerance, tellurite uptake, and biosynthesis of tellurium nanoparticles in hypersaline conditions. Growth and tellurite uptake assays demonstrated tolerance up to 8 mM potassium tellurite, with the removal of approximately 0.45 mM tellurite within 14 days, indicating its potential for tellurium bioremediation. Tellurite stress altered carotenoid biosynthesis, masking the characteristic pink pigmentation. The biosynthesized tellurium nanoparticles were characterized using ultraviolet-visible spectroscopy, dynamic light scattering, zeta potential analysis, electron microscopy, elemental analysis, X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. Their antioxidant activity (DPPH and ABTS assays), antimicrobial efficacy against Gram-positive and Gram-negative bacteria, and biocompatibility towards human keratinocytes (HaCaT) cells were subsequently evaluated. Correlative electron microscopic analyses confirmed the intracellular biogenic synthesis of crystalline tellurium nanorods (50-95 nm in diameter and 160-700 nm in length) composed predominantly of elemental tellurium. The nanoparticles exhibited concentration dependent antioxidant activity (70% DPPH and 62% ABTS radical scavenging at 1 mg/mL), antibacterial activity against both Gram-negative and Gram-positive bacteria, and good biocompatibility toward HaCaT cells. These findings demonstrate that Hgm. borinquense E3 detoxifies toxic tellurite by converting it into multifunctional crystalline tellurium nanorods, highlighting its dual potential for sustainable tellurium bioremediation and nanoparticle biosynthesis with promising biomedical and environmental applications.